- * build_header() (i.e. excludes the IP header). Returns a negative
- * error code if the configuration is invalid.
- */
- int (*hdr_len)(const struct tnl_mutable_config *);
-
- /*
- * Builds the static portion of the tunnel header, which is stored in
- * the header cache. In general the performance of this function is
- * not too important as we try to only call it when building the cache
- * so it is preferable to shift as much work as possible here. However,
- * in some circumstances caching is disabled and this function will be
- * called for every packet, so try not to make it too slow.
- */
- void (*build_header)(const struct vport *,
- const struct tnl_mutable_config *, void *header);
-
- /*
- * Updates the cached header of a packet to match the actual packet
- * data. Typical things that might need to be updated are length,
- * checksum, etc. The IP header will have already been updated and this
- * is the final step before transmission. Returns a linked list of
- * completed SKBs (multiple packets may be generated in the event
- * of fragmentation).
- */
- struct sk_buff *(*update_header)(const struct vport *,
- const struct tnl_mutable_config *,
- struct dst_entry *, struct sk_buff *);
-};
-
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,20)
-/*
- * On these kernels we have a fast mechanism to tell if the ARP cache for a
- * particular destination has changed.
- */
-#define HAVE_HH_SEQ
-#endif
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,27)
-/*
- * On these kernels we have a fast mechanism to tell if the routing table
- * has changed.
- */
-#define HAVE_RT_GENID
-#endif
-#if !defined(HAVE_HH_SEQ) || !defined(HAVE_RT_GENID)
-/* If we can't detect all system changes directly we need to use a timeout. */
-#define NEED_CACHE_TIMEOUT
-#endif
-struct tnl_cache {
- struct rcu_head rcu;
-
- int len; /* Length of data to be memcpy'd from cache. */
- int hh_len; /* Hardware hdr length, cached from hh_cache. */
-
- /* Sequence number of mutable->seq from which this cache was
- * generated. */
- unsigned mutable_seq;
-
-#ifdef HAVE_HH_SEQ
- /*
- * The sequence number from the seqlock protecting the hardware header
- * cache (in the ARP cache). Since every write increments the counter
- * this gives us an easy way to tell if it has changed.
- */
- unsigned hh_seq;
-#endif
-
-#ifdef NEED_CACHE_TIMEOUT
- /*
- * If we don't have direct mechanisms to detect all important changes in
- * the system fall back to an expiration time. This expiration time
- * can be relatively short since at high rates there will be millions of
- * packets per second, so we'll still get plenty of benefit from the
- * cache. Note that if something changes we may blackhole packets
- * until the expiration time (depending on what changed and the kernel
- * version we may be able to detect the change sooner). Expiration is
- * expressed as a time in jiffies.